Oil production method utilizing in situ chemical heating of hydrocarbons



CHEMICALHEATING F HYDROCARBONS Philip J. Closrnrinn and Michael Prats,Houston, Tex.,

assignors to Shell Oil Company, New York, N. Y.,"a corporation ofDelaware No Drawing. FiledNov. 19, 1963, Scr. N 324,843

fiowable nature under normal formation conditions.

This invention constitutes a desirable method for supply! ing heat to anunderground oil-bearing formation for the purpose of increasing the oilrecoverytherefrom.

The" primary production of petroleum hydrocarbon from oil-bearingformations is usually effected by drilling through or into theoil-bearing sand and providing access to the formation through theborehole so as to permit oil' to flow into the borehole from which itmay be recovered by conventional methods and apparatus. If the formationcontains oil of low medium viscosity at reservoir conditions, the 'wellmay -be' produced either by flowing or pumping in a mannerwell known tothe art. If, on

' the other hand, the formation contains a highly'viscous oil atreservoir conditions, it may be necessary to heat the formation in thevicinity of the borehole, to reduce the viscosity of the oil so that theoil may flow into the borehole although asubstantial amount of oil stillre-- mains in the producing formation underground. The residual oil leftin the formation underground is very difficult to produce andconsiderable research has been carried out on secondary recoverymethods.to recover this residual oil. Various methods have been devisedsuch as heating, underground combustion, flooding with water or amiscible fluid, etc. These methods involve injection of water, gas, air,fuel, solvents, etc. or a combination of these into the formationthrough one or more input wells, while the hydrocarbon or componentsthereof are withdrawnthr ough one or more output or producing wells. Theflooding of underground formations -f0r primary or secondary recovery ofhydrocarbon materials,

such as oil, presents many problems, especially intight or relativelynon-permeable formations. 'In the water flooding of an oil-bearingunderground'format-ion, it is neces- -'sary to employ flood water freeof clays, colloidal material, un dissolved salts, etc., which would tendto plug the face of the oil formation and perhaps 'withinthe oilformation itself when the water is injected thereinto. In addition, manyproducing formations being flooded contain a certain amount of swellingclay in the form of a bentonite or montmorillonite clay, which upor'tswelling,

United States Patent 05 ice on. n-onUcrtoN Mentor), UTILIZING IN srruPatentedMay 10, 1966 2 A siblythousands of feet of pipe to the desiredlocation in the well. 1 t It is thereforea primary object of the presentinvent on to provide a method for heating an underground hydrmcarbon-bearing formation in a relatively inexpensive maner so as toincrease the yield of oil from the formation.

Another object of the present invention is to provide a method ofheating an underg ound hydrocarbon-beating formation by means ofinjecting a fluid thereinto which does not have to be heated at thesurface before pumping it down the well.

'A further object of thepresent invention is to provide method for theprimary or secondary recovery of oil from a formation by injecting aheat-creating chemical i.c., one. that reacts exothermic-ally in theformation with the hydrocarbon contained therein.

Still another object of the present invention is to provide a methodwhereby permeable flow channels may be formed extending outwardly from'a well, or extending between at least two wells, in a manner such thatordinary or presently-known flood methods can be carried out betweenwells penetrating the formation after the permeable channels have beenformed.

Anotherobiect of the present invention is to provide amethod for heatingan underground oil-bearing formation Y without the necessity ofemploying heating equipment at the well site.

A still further object of tlse present invention is to provide a methodof increasing the permeability of the obviates the hazard encountered ininjecting a gaseous."

reactant at .a pressure sufficient to form fractures in the formation.

These and other objects ofthis invention will be understood from thefollowing description.

The method according to-the present invention contem- I plates producingliquid or liquifiable hydrocarbons from a hydrocarbon-bearing subsurfaceformation which is penetrated by one well, by introd'ucinginto the wella quantity of solid-free liquid reactant which reacts exothcrmicallywith hydrocarbons, confining the liquid reactant reduces thepermeability of the formation. The use of i solvents as a flood or theuse of chemicals added to the water for flooding a formation is oftenprohibitive in cost. Additionally, many of the oils left inthe'formation are very viscous and it is essential that they be heatedin order to cause them to flow to a producing well. While under-- assteam, hot water, hot ,solyents, etc. in the formation,

the heating of the flooding material at the surface is expensive and ofcourse there is some heat loss in trans. milling the heated materialfrom the surface down pos- Further, while forma in the well opposite aselected interval of the hydrocarboncontaining formation, applying apressure to the liquid reactant sufficient to force it into thehydrocarbon-' containing formation, maintaining the liquid reactant insitu for a time sufiicient for the liquid reactant to reactexothermically with a portion of the hydrocarbon of the formation andheat the hydrocarbon-containing formation adjacent the well and/oradjacent fractures formed in the format-ion, and subsequently producingoil from the heated formation. In some cases, the liquid reactant isforced into the formation at a pressure at which the formation isfractured While being supplied into the fraeture in a quantitysufficient so that the liquid reactant is forced into the walls formingthe fractur This method of generating heat in an oil-bearing formationby means 'of a liquid reactant is especially suitable for selectivelyheating a limited region or selected location. within an oil reservoirformation. When using a liquid reactant as a heat-creating medium, theneed for heating equipment at the well'site is avoided. A liquidreactant is superior to a gaseous reactant as the useof a gaseousreactant would necessitate the use of expensive high pressurecompressing equipment at the wellhead.

The liquid reactant is allowed to remain in the formation for a timesufficient to heat the desired portionof the formation. The heating ofthe reservoir formation I I need only be sufiicient to move thepetroleum within the selected region of the formation or to put thepetroleum in a condition that it will move readily from the formationwhen the well is produced. The'deg'ree to which the oil mobilization isattained can readilybe determined by applying a pressure gradientacrossthe selected region,

formation of'fracturesdoes not create either a hazard or ,a significantdisadvantage as would the case be if the reactant were a gas.Preferably, the injection wellis opened at a point opposite theoil-containing reservoir formation to' communicate with a verticallyextensive interval of the reservoir formation to encourage uniform-penetration and/or vertical or horizontal fracturing. After injectingaselected .volume of liquid reactant, for

example 200 barrels, into a f'ormationhaving a thickness of feet, thewell is shutin at the injection pressure. well is reduced so as toinitiate backfiow of oil into the well; The backfiow results from thepressure drop be:

tween the injection pressure, or the formation fluid pressure, ahd the'pr'essure'within the well. The wells can be swabbed or pumped to reducethe pressure in the well to substantially atmosphericv pressure, ifdcsired.-

Thismethod of thermal soaking of a formation with a liquid reactant cantake place in a single well which would be used both as an injection anda production well.

Fracturing of the formation may or may not take place during the thermalsoaking process. Thermal soaking of a well permits producing a highviscosity oil from a reservoir that has a significant but lowpermeability. The

liquid reactant, is preferably a liquid oxidant which isinjected intothe reservoir and maintained there for a time sufficient to oxidizereservoir oil and-heat the reservoir prior to 'producinga reservoir. inmost reservoirs significant advantages can be obtained by injecting afluid containing a higher concentration of oxidant than can be feasiblyobtained from a free-oxygen-containing gas. Since it is undesirable toinject a gas into a reservoir at a pressure exceeding the overburdenpressure, a liquid reactartt or a liquid phase oxidant in accordancewith the present-invention is advantageous.

- The method of the present invention can also be em ployedin oil fieldscontaining at least two wells which penetrate an oil-bearing formationof significant but low permeability wherein the liquidoxidant wouldbe'injected through one well, into the formation and thence 'to the;produc tiori well. An example of this modification of the presentprocess is given. A well completed into a tar sand of significant butlow permeability is freed of or ganic material by circulating a slug ofhydrocarbon vsolvent followedby a slug of aqueous liquid containing adetergent. A slug of fresh water is then injected into the formationwhile fluids are withdrawn from an adjac'ent production well that iscompleted into the same reservoir at a distance of, for example, 50feet. In a ,typical'situation about 400 barrels of 5% aqueous hyrogenperoxide would be injected into the well and into the oil-bearing'tarsand. The hydrogen peroxide injection might required about 1 to 2weeks and the peroxide is left in the formation about'l to 2 months.Fluids are then produced from the heated reservoir by means of secondaryrecovery methods suitable for an oil of about medium viscosity.

After such a soaking, the pressure within the tensive portion of theformation around the well.

In the preferred modification of the present invention, a pressure isapplied. to the liquid reactant in the. well which is sulficient to formfractures in the formation extending outwardly from the well. thenforced into the fractures and into the formation forming the walls ofthe fractures to heat a radially ex- When at least two wells areinvolved a pressure may be 'sub' sequently applied to the liquidreactant sufficient to extend the-fractures to a second well with thepressurebcing maintained-at a value sufficient to maintain the fracturesopen in the absence of propping agents/whereby the hydrocarbons in theformation forming the walls of the fractures are heated; i

In the event that the fractures extending from the injection well didnot extend all the way to the production well, the fracture into whichthe reactive liquid was i-njected can be subscquentlyswept free ofthespent reactant and the oil of reduced viscosity by liquid displacementof th se 'fiuids into the formation or by allowing themto drain back tothe injection well., Subsequently, the fracture could be retreated witha new quantity of liquid reactant to remove'more of the oil from theformation,

which step could be repeated, as needed. In the fnormalIy-porous'reservoir formations that are plugged with-viscous oils, a removal ofthe'oil contained in the walls of the fracture createst a permeable paththrough the-reservoir formation. As soon as such a permeable I path orlayer has obtained a thickness of a few inches,

the reservoir formation can be readily heated and produced byconventional thermal drive procedures, such as Liquid reactant is steamor hotwater injections, which, because of the permeable path,are notdependent upon propped fractures or injection pressures that exceed theoverburden pressure of the depth of the-reservoir. Thus, once the oilhas been removed from the wallsurrounding a frao-' ture to form apermeable flow path along the fracture,

the pressure at which the liquid reactant was injected can be reducedbelow that needed to hold the fracture ,open.

A modification of the heating and fracturing process a describedhereinabove would permit a fracture extending from the injection well,after being freed of organic anaterial, to have water injected into itat a pressure and a volume sufiicient to extend the fracture to, theproduction well. The water would then be displaced from the fracture byinjecting enough hydrogen peroxide through the injection well andfracture to cause a layer of hydrogen peroxide to-be produced at theproduction well.

The rate of hydrogen peroxide injection ismaintained until the front ofthe concentrated solution of hydrogen peroxide reaches the productionwell, at which time injection is stopped and the peroxide reactant isallowed toremain in the formation for a one to two month period in orderto heat the entire formation. I

A liquid phase reactant or oxidant may beemployed which reactsexothc'rmically with the oil of the formation. This for example hydrogenperoxide, nitrous oxide, sulfur trioxide, etc., and liquids containingthese materials are suitable. If sulfur trioxide is to be used it ispreferably in the form of oleum,.i.e. concentrated sulfuric acid havingan excess of sulfurtrioxide present. Clear solutions rather thansuspensions must be employed as suspensions of material are undesirableas the solid mate rial in the suspension filters out on the surface ofthe borehole wall and limits .or prevents further injection of fluidinto the formation. Nitrogen oxides which are used in accordance withthe present invention are used in a reservoir in which the overburdenpressure is a value which the nitrogen oxide forms an aqueoussolution.Nitrogen'oxide may be used in the form of fuming l'lllllC acid. Thus thereactants that are contemplated for use in the presentproccss comprisesingle phaseliquid systems which are readily injected into the earthformations.

In respect to using oleum in fractures in the formation at which thenitrogen oxide being usedjis liquid, or at I t a in accordance with thepresent method, the fracture would be tmmediately heated by the heat ofhydration and/or neutraliiation released as the oleu'mdisplaces anaqueous fracturing fluid andlonan'ywater in the pores of the formation.When a layer of oleunt extends from an injecuon well tothe vicinity of aproduction well, the

injection of the oleum is preferably stopped to prevent its flowout ofthe formation and the oleum is allowed to complete its reaction with thehydrocarbons in'the wall ofthe-fractures. After allowing this reactionwith its. concurrent heating to occur, the spent oleum maybe displacedor contacted with caustic, thus causing further heating withintheformation due to neutralization of the unreacted sulfuric acid.- Thisaction would also enhance the emulsification of the oil in the injectedliquids due to the surfactant properties of thesalt s of the sulfonatedaromatic compounds formed by the reaction of some of the' sulfurtri'oxide with a p'ortion'of the hydrocarbons in the formation, Thismethod of heatingisparticularly advantageous in that the heat isgenerated in situ all along the walls of the fractures that maypenetrate deeply into, the formation. It provides a means for relativelyquickly heating a substantial volume of 'an oil-bearing reservoir. Asindicatedhereinabove, a liquid phase reactive fluid comprises aparticularly advantageous means of chemically heating portions of anunderground reservoir formaform fractures in said hydrocarbon-containingformation, 1 subsequently maintaining said liquid reactant in saidfractures for a time sufficient for the liquid reactant to reactexothemically with a portion of said hydrocarbon of said formation andheat the hydrocarboncontaining formation adjacent the well, andsubsequently prociuc hydrocarbon-containing, formation adjacent thefractures to form permeable flow channels in said formation along saidfractures 2. The method of 1 wherein the hydrocarbons are 'i 4 producedback into the wellby discontinuing the applica" tion of pressure to theliquid reactant and opening the well in a manner permitting flow'ofhydrocarbon into the well. 1

3. Die method of ciaim 1 carried out inone well positioned in thevicinity of a second or production well wherein the hydrocarbonsare-produced into said second well by maintaining a pressure on theliquid reactant forced into said formation.

tion because it is dangerous to injecta gas at pressures exceeding theoverburden pressure of the reservoir formation. The use of liquid isadvantageous because the pressure applied to them is immediately reduced(by the effects within the formation) whenever fracturing occurs.

In contrast, a gas, which is a relatively extensively compressiblefluid, would immediately expand into the greater- 'volu me madeavailable by the fracture and would continue to exert a relatively high-pressure in a manner liable to cause .a' blowout through the surface.Blowouts,

especially around a well casing, have been eliperien'ced when using agas asan injectioniluid in a formation.

As compared to gases, liquid reactants have theadditional advantages ofrequiring materially less equipment and energy to provide a given highinjection pressure and also have thefl capability of containing a muchgreater mass of reactants per unit volume. I

The method of the present invention is not concerned with heating aformation to ignition temperature of'the oil to carry outsecondary'recovery of oil by underground combustion methods.v This highdegree of heating is not pertinent to thepresent process. All thatneeded is a temperature rise sufiicient to move a localized portion ofthe oil adjacent the well or the fractures extending therefrom. Theamount of heating obtained by the present method does not cause crackingor distillation of oil in the reservoir. It need only render the oilsusceptible to fluid displacement and/or entrainment by the reactantliquid and/or other fluids that are subsequently pumped through ordisplaced within the selected portion of the reservoir formations. I

We claim as our invention: l. A method of producing liquid orliquifiable hydro carbons from a hy drocarbonvcontaining subsurfaceformasaid methodcom'prising:

introducing into a well-a quantity of a solids-free liquid.

reactant which reacts exothermically with hydrocarbons-,

' confining said liquid reactant in said well opposite a- .selec tedinterval of said hydrocarbonecontaining formation,

applying a pressure to said liquid reactant sutficient to tion,said'formation being penetrated by at least one well,

4. The'method of claim 1 including the step of applying a pressure tosaid iiquid reactant sufficient to extend" said fractures to a secondwell, and maintaining said pressure at a yalue snficient to maintainsaid fractures open in the absence of propping agents whereby thehydrocarbons in the formation forming the wallsof the fractures areheated. 1

5. The method of claim 4 including the step of producing heatedhydrocarbons from the fractures 6. :l'h'e method of claim 5 includingthe step of increasing the permeability of the hydrocarbon-containingformation adjacent the fractures throughout the length thereof byinjecting additional liquid reactant until a chemically-heated permeabletlow channel is formed through said formation adjacent the fractures,and subsequently reducing the injection pressure below that necessary tomaintain the fractures open while being sutiicient to force fluidthrough the permeable flow channels formed in the formation. p I. Themethod of claim 6 including the step of sub sequently producing thehydrocarbon-containing formation by injecting a hon-reactant fiuid inone well under orrnzn REFERENCES- 7 Uren, Petroleum ProductionEngineering, Oil Field Exploitation, 2nd Edition, McGraw Hill Book Co-.,Inc., N.Y. (l939),pages376-379 relied on.

CHARLES E. O'CONSELL, Primary Examiner.

BENJAMIN 111211511, Examiner. 4 S. I NOVOSAD, Assistant Examiner.

g hydrocarbons from the heated pressure so that it drives hydrocarbonsto said second

1. A METHOD OF PRODUCING LIQUID OR LIQUIFIABLE HYDROCARBONS FROM AHYDROCARBON-CONTAINING SUBSURFACE FORMATION, FORMATION BEING PENETRATEDBY AT LEAST ONE WELL, SAID METHOD COMPRISING: INTRODUCING INTO A WELL AQUANTITY OF A SOLIDS-FREE LIQID REACTANT WHICH REACTS EXOTHERMICALLYWITH HYDROCARBONS, CONFINING SAID LIQUID REACTANT IN SAID WELL OPPOSITEA SELECTED INTERVAL OF SAID HYDROCARBON-CONTAINING FORMATION, APPLYING APRESSURE TO SAID LIQUID REACTANT SUFFICIENT TO FORM FRACTURES IN SAIDHYDROCARBON-CONTAINING FORMATION, SUBSEQUENTLY MAINTAINING SAID LIQUIDREACTANT IN SAID FRACTURES FOR A TIME SUFFICIENT FOR THE LIQUID REACTANTTO REACT EXOTHERMICALLY WITH A PORTION OF SAID HYDROCARBON OF SAIDFORMATION AND HEAT THE HYDROCARBONCONTAINING FORMATION ADJACENT THEWELL, AND SUBSEQUENTLY PRODUCING HYDROCARBONS FROM THE HEATEDHYDROCARBON-CONTAINING FORMATION ADJACENT THE FRACTURES TO FORMPERMEABLE FLOW CHANNELS IN SAID FORMATION ALONG SAID FRACTURES.